Vehicles with an internal combustion engine may be fitted with fuel vapor recovery systems (evaporative emissions control systems) wherein vaporized hydrocarbons (HCs) released from a fuel tank are captured and stored in a fuel vapor canister containing a quantity of fuel-absorbing material such as activated charcoal. Eventually, the fuel vapor canister may become filled with an amount of fuel vapor. The fuel canister may be cleared of fuel vapor by way of a purging operation. A fuel vapor purging operation may include opening a purge valve to introduce the fuel vapor into the cylinder(s) of the internal combustion engine for combustion so that fuel economy may be maintained and fuel vapor emissions may be reduced.
Activated charcoal has been found to be a suitable fuel vapor adsorbing material to be used in such a canister device because of its extremely porous structure and very large surface area to weight ratio. However, this porous structure can lose some of its adsorption efficiency when coated with liquid fuel or water. In one example, during a refueling event a pump operator may add fuel after an initial automatic shut-off. For instance, in an attempt to maximize the amount of fuel pumped into the tank, a pump operator may dispense additional fuel in what is commonly referred to as “trickle-filling”. If liquid fuel has entered the fuel vapor recovery lines (evap recovery lines) and a purge cycle is commanded at the next engine start, the liquid can get sucked into the canister and corrupt the activated carbon. In another example, water can enter the canister via a vent line during a purging operation and/or during driving through a flooded area or backing up a vehicle during a boat launch procedure. As vehicle strategy typically purges most of the time during vehicle operating conditions, sealing the evaporative emissions control system and discontinuing purging operations during conditions of high humidity may prevent water from being routed to the canister.
U.S. Pat. No. 6,003,498 teaches a fuel vapor canister purge control strategy in which canister purging operations are adjusted during high humidity conditions. High humidity conditions are detected by monitoring hardware normally available on the vehicle, such as windshield wiper switch state and transmission gear state. In one example, responsive to an indication of an active state of a windshield wiper switch, it is presumed that the vehicle is operating in a high humidity environment, and thus the purge system is disabled to minimize moisture intrusion. Other examples include adjusting purge rate as a function of indicated wiper speed, allowing the purge system to be selectively disabled only during periods of significant rainfall when moisture contamination of the fuel vapor adsorbing material is likely. However, the inventors herein have recognized potential issues with such a method. For example, there may be circumstances wherein the potential for water ingestion into the fuel vapor canister is high, yet the windshield wiper switch may or may not be activated. Examples may include driving through heavy water or during launching a boat. During conditions such as these, correlating canister purge control with windshield wiper state may not always prevent the undesired ingestion of water into the fuel vapor canister.
Thus, the inventors herein have recognized the above issues, and developed systems and methods to at least partially address the above issues. In one example, a method is provided comprising, during vehicle operation, monitoring tire pressure in one or more vehicle tires, and responsive to a tire pressure decrease greater than a threshold, sealing the evaporative emissions control system and suspending purging of the fuel vapor canister.
As one example, barometric pressure may be monitored via a barometric pressure sensor positioned in the engine intake manifold, and the evaporative emissions control system may be sealed and purging of the fuel vapor canister suspended responsive to a tire pressure decrease greater than the threshold, and an absence of a change in barometric pressure. In this way, a change in tire pressure that is not associated with a corresponding change in barometric pressure may be attributed to a cooling of the tires resulting from tire exposure to water, and the evaporative emissions control system sealed accordingly. By sealing the evaporative emissions control system (ceasing venting of the emissions control system) and suspending purging of the fuel vapor canister responsive to an indication of tire exposure to water, fuel vapor canister functional lifetime may be increased, and undesired evaporative emissions prevented.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.